Misplaced Nail on Thoroughbred Mare: Case Study

"Who here has never stuck a horse (driven a nail into sensitive areas when shoeing)?" asked host Ric Redden, DVM, founder of the International Equine Podiatry Center in Versailles, Ky., during the 16th annual Bluegrass Laminitis Symposium. Only a very few out of the 550-plus attendees (mostly farriers) raised their hands, showing that the following problem could happen to anyone.

Julie Grohs, DVM, of the Alaska Equine and Small Animal Hospital in Chugiak, Alaska, presented the following case study of complications following a misplaced nail in a Thoroughbred hunter/jumper mare. Initially the 7-year-old mare was in excellent physical condition with no history of lameness, but became sore the evening of a reset with commonly used, very wide-web shoes. The farrier returned that evening to reset the shoes and lower the nail holes, and commented to the trainer that the previous holes might have been too high in the feet.

The mare seemed more comfortable after the reset, and the trainer administered a non-steroidal anti-inflammatory medication (NSAID) following veterinary consultation. The mare responded well, but two days later the right front shoe came off and she was acutely lame on that foot. At this point Grohs first examined the mare.

Initial Presentation

At the time of the exam, the mare was grade 4/5 lame on the American Association of Equine Practitioners (AAEP) scale (obvious lameness at a walk) in both front feet. Both front feet also had heat and increased digital pulses, and the soles were flat and easily compressible with only nine millimeters of sole (most consider 15 millimeters to be a minimum for soundness). Based on previous radiographs, this thin sole depth was apparently normal for the mare, but she had been trimmed shorter than usual this time. The positions of her coffin bones were normal.

See photos of the mare's initial presentation and subsequent complications here.

Insulation foam was applied to both feet, and the mare was put on stall rest and acepromazine (for vasodilation and calming) for five days. This appeared to help until eight days later, when the mare suddenly became severely (non-weight-bearing) lame on the left front foot.

At that point, the possibility was considered that the mare had become caught in the stall mats because of construction commotion in the area and stall mat disarray. There were strong digital pulses in both front feet, and she was grade 5/5 lame on the left front foot (minimal weight bearing in motion and/or at rest or a complete inability to move). She exhibited pain on flexion of that limb and to hoof tester pressure over the heels, and no abscess could be located. No changes were apparent on radiographs.

"Differential diagnoses at this time were continued inflammation from recent trimming predisposing to a laminitic event, possible abscess, and/or new trauma (ligament injury or fracture)," said Grohs.

The left front foot lameness continued, escalating until the limb was casted for transport to the equine hospital. Casting improved her comfort level, and upon removal, drainage (indicating an abscess) was found at the lateral (outside) heel. The drainage tract was opened and ceftiofur (an antibiotic) and NSAID treatment was begun. This treatment was unrewarding, with the mare continuing to spend a lot of time lying down. She began developing pressure sores, then radiographs showed osteolysis (bone dissolution) of the lateral edge of the left front coffin bone.

Surgical Treatment

"At the time that acute osteitis was diagnosed, the decision was made to take the mare to surgery to remove affected portions of the distal phalanx," said Grohs. The procedure was performed with the mare standing, blocked, and sedated, with a farrier more experienced with critical cases assisting with resection of the affected area. Tracts were found that were clearly associated with the lateral nail holes, said Grohs.

"The underlying laminar tissue was grossly abnormal in appearance," she said. "It was dark purple in color and did not bleed (indicating a lack of active blood supply)." The affected bone beneath, an area about 20x30 mm and 5-10 mm deep, was removed. The site was packed with silver sulfadiaziene (an antibiotic) and gauze, wrapped with an elastic bandage, and covered with a hospital plate that had a lateral side covering plate added.

The material removed from the hoof contained Escherichia coli and Streptococcus zooepidemicus, both of which were found to be insensitive to ceftiofur (hence the poor response to earlier antibiotic treatment with this agent) and sensitive to gentamicin. The mare's antibiotic regimen was changed to gentamicin.

The mare still did not become more comfortable until a cast was applied over a cuffed wedge shoe, at which point she began spending the majority of her time on her feet. The right front remained in a cuffed wedge shoe with impression material to stave off supporting limb laminitis. Two weeks after applying the cast to the left fore, it was removed and the resected area had about 15 mm of hoof growth. The mare was discharged from the hospital about two months after the original injury, and she was confined to stall rest wearing cuffed wedge shoes on both front feet while remaining on a medical regimen of NSAIDs and cimetidine (an anti-ulcer medication).

About two weeks later, the mare became very lame on the right front along with hives possibly related to a feed change. Radiographs showed rotation of the coffin bone, which was initially treated with a rail shoe and impression material. The mare's initial response was encouraging, but "five days later there was an obvious bulge above the coronary band on the dorsolateral (front outside) surface of the foot that was very painful to palpation," said Grohs. A lateral radiograph showed inflammation on the dorsal surface of the coffin bone, a gas/fluid line at the coronary band, and an area of separation below the coronary band with constriction below. A heart bar shoe with impression material under the shoe and on the ground surface was applied, and the hoof wall was grooved horizontally below the bulge. This seemed to help initially, but the mare relapsed; a second groove above the first collapsed immediately (indicating a very unstable hoof).

The mare was hospitalized again, and a venogram showed a "loss of blood flow on the dorsal hoof wall and displacement of the circumflex artery from ventral (solar, or beneath) to the tip of P3 (the coffin bone) to cranial (in front of) the tip," said Grohs. This indicates rotation of the coffin bone past the blood supply that normally runs beneath it. "The tip of P3 was very close to coming through the sole. The decision was made to cut the deep digital flexor tendon (to release the rotational pull on the coffin bone) on the right front. The dorsal hoof wall was thinned out with a dye grinder short of doing a complete resection. Within days, the bulge above the coronary band disappeared and the mare became significantly more comfortable."

Follow-Up

"The left front hoof has grown substantially and the mare is very comfortable on that foot," reported Grohs. "The right front hoof was still slightly uncomfortable, but had a few millimeters of growth at the coronary band and had gained 6 mm of sole by the end of September (this problem started last spring). Radiographs revealed good growth of sole. Shoes are being periodically reset to maintain breakover and avoid toe pressure. The owner was allowed to begin a minimal hand-walking program of five minutes every other day in November. At that time the mare was sound at the walk on the left front foot and grade 3-4/5 lame on the right front foot."

Grohs updates us on the mare in early March: ï¿½She is doing great. I am almost ready to allow her to start a longeing program. She is on her feet almost all the time and is very rambunctious while hand walking. Her soundness is improving weekly, and hoof growth appears normal.

Lessons Learned

"From the presenting signs and history available at the time of the first examination of this horse, the probable diagnosis was sore feet from being trimmed too short," Grohs reflected. "As time wore on and this horse's condition deteriorated, other possible diagnoses and causes had to be considered. Further discussions with the trainer revealed that when the farrier reset the shoes to lower the nail holes, a small amount of blood was seen on the floor. The shoes used had nail holes that were punched very deep. It is possible that on a thin-walled Thoroughbred, especially if the walls had been overdressed previously and with an overzealous trim, that the result with such a shoe would be a nail or nails placed too deep, thus contaminating the internal aspect of the hoof capsule, leading to acute osteitis. The nail placement as the cause of infection was confirmed at the time of surgery.

"Farriers, if you suspect you have misplaced a nail, especially if bleeding occurs, inform the owner or handler and request that the veterinarian be called," she recommended. "Ask for permission to speak directly to the veterinarian to provide detailed, accurate information about the horse. Next, pack the hoof with antiseptic and protect it from contact with the ground. It will be important to determine whether the horse has had tetanus prophylaxis. Veterinarians, respond to these calls quickly and give them your full attention and concern. Communication with the entire care team for the horse is essential to try to avoid this serious and potentially life-threatening situation.

"Most veterinarians have encountered situations like this one at some point in their careers," she went on. "The risk involved in trimming hooves and nailing on shoes is inherent in the task." When a misplaced nail is suspected, "it is imperative that the farrier take the responsibility to inform the owner or trainer immediately that there is a risk and request (and in some cases demand) that the veterinarian be called. If you think that contaminating the foot isn't a big deal, you could be so, so wrong. Second, professional farriers should be actively engaged in continuing to develop the art of the horseshoer into the science of the podiatric farrier. It is important that veterinarians and farriers speak the same language and that we converse regularly and in detail to share information.

"Third, as a team we should make every effort to educate our mutual clients about the importance of hoof health and what we can and should do together to improve and maintain that aspect of hoof health," she concluded.

FURTHER COMMENTS

Redden had a few additional comments on this topic during the question and answer session.

When you suspect a misplaced nail, look for a low nail, not the highest one--that is likely the most carefully driven one in the whole foot.

If you've misplaced a nail and the foot is bleeding out of the sole, don't set it down--that will pack dirt in the wound.

Hot-seating a shoe can help kill surface bacteria.

If you've misplaced a nail, immediately put on antibiotic and don't drive another nail within an inch of the spot (that can push the soft inner tissues to close the wound and seal in bacteria). Recommend not sending the horse to any performance events in the short term.

A "hot nail" can be a legal responsibility as well as a moral/ethical one.

Redden recommends packing a hot nail hole with dimethyl sulfoxide (DMSO) and Betadine (iodine scrub), then packing the hole with a cotton ball.

If you see exudate 24-48 hours after you shoe a horse, that's not from your hot nail, but from a problem that was already brewing.

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